Yes, I searched a couple of times for such script. It was strange because there is KillAll script but not KillCreature. And I can't seem to find a script to do damage to a creature in combat. Is there something like that?

Oh, I saw that there is add a creature to the current encounter. But here is no remove.

All migthy fine ideas and I think we should have a suite of scripts for setting up creature number and condition prior to the start of an encounter. I will prepare such as well as following up with adding a new type of ally that will not become a party member and will only exist for one battle (player controlled, not limited how many of such allies will be added, no portratits, no access to inventory or detailed stats).